The present disclosure relates to systems and methods digital modulation and demodulation of data in a fiber optic communications system.
Fiber optic channels in network communications systems are well known and are considered effective for data transmission, allowing relatively high bandwidth data communication. Optical fiber used in such channels is flexible and can be bundled as cables, and is generally considered to be appropriate for long-distance communications because light propagates through the fiber with little attenuation compared to electrical cables. Typical present day commercial optical fiber systems transmit data at 10 or 40 Gigabit-per-second. Each fiber can carry multiple independent channels, each using a different wavelength of light in a technique known as wavelength-division multiplexing or WDM, thereby enhancing the net data rate of an optical fiber.
As more capacity is continually desired for networks, a demand for increased data transmission rates exists. However, in fiber optic systems, as data rates increase various optical phenomena begin to manifest and act to limit data transmission rates. For example, chromatic dispersion and polarization mode may affect the ability of a receiver to demodulate and decode a transmitted optical signal. Forward error corrections (FEC) schemes are often used to send redundant data to address these issues, as well as others.
Low-density parity check (LDPC) codes have been used as an effective FEC scheme in different areas of communications. The use of LDPC codes in high speed optical communications, however, may present some challenges because of the latency associated with the iterative decoding process.